Glass drawing kiln l-block



Feb. 7, 1967 c. R. WARD GLASS DRAWING KILN L-BLOGK Original Filed Sept. 30, 1960 5 Sheets$heet 1 Faai PRIOR ART INVENTOR. C [C/L 1Q. WARD Feb. 7, 1967 c. R. WARD 3,303,012

GLASS DRAWING KILN L-BLOCK Original Filed Sept. 30. 1960 5 Sheets-Sheet 2 IN VEN TOR.

C5674 R. WARD BYQMXZ ATTORNEY Feb. 7, 1967 c. R. WARD 3,303,012

GLASS DRAWING KILN L-BLOCK Original Filed Sept. 30. 1960 5 Sheets-Sheet 3 'INVENTOR.

CFC/L /2. W420 BY @MX%M A TTOE/V' Y Feb. 7, 1967 c. R. WARD 3,303,012

GLASS DRAWING KILN L-BLOCK Original Filed Sept. 30. 1960 5 Sheets-Sheet 4 IN VEN TOR.

CECIL 2. WARD rITTOR/VEY Feb. 7, 1967 c. R. WARD 3,303,012

GLASS DRAWING KILN L-BLOCK Original Filed Sept. 30. 1960 5 SheetsSheet 5 0' P8 E o 3 --g; j I I l INVEN TOR. C'C/L /z WARD h a' 3 ATTORNY United States Patent 3,303,012- GLASS DRAWING KILN L-BLOCK Cecil R. Ward, Gibsonia, Pa., assignor to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Original application Sept. 30, 1960, Ser. No. 59,743, ow Patent No. 3,208,842, dated Sept. 28, 1965. Divided and this application Feb. 12, 1963, Ser. No. 258,052 1 Claim. (Ci. 65193) This application is a division of my copending application, Serial No. 59,743, filed September 30, 1960, now Patent No. 3,208,842 entitled, Glass Drawing Apparatus.

This invention relates to the manufacture of sheet glass by continuous drawing from a bath of molten glass and provides improved methods and apparatus for producing drawn sheet glass of improved appearance wherein the usual characteristic wave pattern, i.e., transverse thickness variations which appear as bands of ribs, extending generally in the direction of the draw, is eliminated or materially reduced.

These characteristic wave pat-terns primarily occur because of non-uniform cooling of the sheet across its width. To provide uniform cooling of the sheet, it is desirable to allow the heat loss to take place substantially entirely by radiation rather than by a transfer to convection currents or a combination of radiation and a transfer to convection currents.

In conventional processes of drawing sheet glass, a natural stack is induced by the geometry of the sheet, bath and drawing chamber wherein there is a transfer of heat from the bath and sheet at relatively elevated temperatures to the cooler ambient air within the chamber producing a convection flow of air in the direction of the draw and out of the chamber. The movement of the heated air in the direction of the draw results in zones of reduced pressure at the base or meniscus of the sheet, so that colder air is drawn to the reduced pressure zones. Air enters the drawing chamber at the juncture of the chamber and the drawing machine and leaks into the chamber from cracks, crevices, or the like in the chamber walls. Colder air flowing to the zones of low pressure is chilled by moving generally across coolers, which are disposed within the chamber slightly above the surface of the bath and on the opposite sides of the sheet to accelerate the setting of the glass. As readily understood, the temperature of entering air will be non-uniform because of differences in temperature of the sources of this air, and this condition will persist due to diiferences in paths taken by this air in the drawing chamber and, also, due to conditions within the kiln. These temperature differences cause nonuniform velocitie within the drawing chamber. The colder air of non-uniform velocities flows to the reduced pressure zones and disturbs the relatively thin surface adhering film moving with the glass causing nonuniform heat transfer across the sheet, thereby affecting the formation of the glass in the area where the glass undergoes the transition from fluid to solid state. Being in the plastic state and under stress, the glass is unequally attenuated to form a characteristic longitudinal wave pattern.

Another characteristic wave pattern extends diagonally and usually exists on the outer margins of the sheet. This diagonal wave pattern may be so severe, in some instances, as to extend entirely across the sheet. The diagonal wave pattern, when superimposed on a longitudinal wave pattern, provides a pattern referred to in the sheet glass industry as batter or dapple, and is the result of currents of colder air flowing from the vicinity of the ends of the coolers and the ends of the drawing chamber to the zones of low pressure at the base of the sheet.

ice

These currents of air are commonly referred to as endaround currents.

Many arrangements have been proposed to improve the appearance of drawn heet glass. One such arrangement is taught by Brichard in United States Patent No. 2,693,- 052 wherein burners or suction means are disposed just above the surface of the bath to eliminate flow of relatively cold air to the base of the glass sheet and to eliminate flow of air along the sheet in the direction of the draw. Thus, either no air flow takes place along the sheet or else such air flow as takes place moves along the sheet in a direction opposite to that of the draw.

It has been found that the appearance of drawn sheet glass may be materially improved if, instead of eliminating the flow of air to the base of the sheet, the flow of air to and from the base of the sheet is controlled or regulated, so as to be diminished but not eliminated. This control or regulation of the flow of air to the base of the sheet does not eliminate but reduces the flow of air along the sheet in the direction of the draw. The latter how of air forms an undisrupted uni-directional protective layer or envelope surrounding the sheet and moving at a velocity sufficiently low so that it does not disturb the relatively thin insulating surface adhering film of air surrounding the sheet. This reduction of flow of air to and from the base of the sheet eliminates or materially reduces the non-uniform disturbance of the relatively thin surface adhering film of air surrounding the sheet, so that variations in attenuation of the sheet are materially reduced, thus providing an improvement in the appearance of the sheet.

The provision of a protective envelope of air moving at a sufficiently low velocity in the direction of the draw results in a minimized cooling of the glass sheet by heat transfer through convection currents and thereby allows more uniform cooling of the sheet by radiation to the usual coolers spaced from the sheet and located slightly above the surface of the bath of molten glass. The endaround currents are also reduced and/or rendered ineffective, so that the usual diagonal wave pattern is eliminated. Thus, a method and apparatus have been devised for eliminating the undesirable effects of air currents which naturally occur in a sheet glass drawing device while retaining their desirable effects. Stated somewhat dilferently, a method and apparatus have been devised for reducing the flow of air to and from the base of a glass sheet being drawn to such a degree as to minimize undesirable effects, while retaining sufiicient flow of air so as to form a protective envelope surrounding the sheet in the direction of the draw and obtain new desirable effects.

Briefly, the invention herein disclosed utilizes novel means for creating a stack effect upon the air within the drawing chamber behind each cooling member, in this way counteracting the normal cyclic movement of cool air between the cooling members and the remote parts of the drawing chamber which would, if not diverted, cause an uneven cooling of the glass sheet in the critical forming zone.

Therefore, the primary object of this invention is the provision of improved methods and apparatus for improving the appearance of drawn sheet glass.

Another object of this invention is the provision of methods and apparatus for eliminating the undesirable effects which occur in a sheet glass drawing chamber because of the natural air currents while retaining the desirable effects of these air currents, thereby materially improving the appearance of the sheet being drawn.

A still further object of this invention is the provision of improved method and apparatus for controlling and regulating air currents within drawing chambers which may be readily utilized indifferent apparatus with substantially uniform results and without interfering with the normal operation of the apparatus.

Other objects and features of this invention will be apparent from the following description and the appended drawings, which illustrate various embodiments of the invention and in which:

FIG. 1 shows diagrammatically a drawing kiln of conventional, prior art construction and the flow of principal air currents therein;

FIG. 2 shows diagrammatically a first embodiment of a drawing kiln according to this invention and the flow of principal air currents therein;

FIG. 3 showsdiagrammatically a second embodiment of this invention and the flow of principal air currents therein;

FIG. 4 shows diagrammatically a third embodiment of this invention and the flow of principal air currents therein;

FIG. 5 is an isometric view of the construction of a recessed L-block.

FIG. 6 is an isometric view of a cooling member with sheet backing material mounted thereon.

Turning to the drawings wherein like parts are identified with like reference characters, there is shown in each of FIGS. 1-4 a sheet of glass 10 being drawn from a bath 12 of molten glass in a drawing kiln generally indicated at 13 (only parts of which are shown but which is a conventional construction). A draw bar 14 extending transversely of the kiln 13 is submerged in bath 12. The glass sheet 10 in its viscous condition forms a base or meniscus 16 with the surface of the bath 12, and the sheet 10 is drawn from the bath 12 and through the drawing chamber 22 of a kiln 13 by means of drawing rolls 18 of a conventional drawing machine generally indicated at 20. The drawing chamber 22, as depicted in the drawings, is defined by bath 12 and conventional L-blocks 24, ventilator water coolers 26, end walls 28 and catch pans 30. The ventilator coolers 26 are each positioned between an L- block 24 and the base framework of the drawing machine and extend substantially to the end walls 28 of the kiln 13. The base of the drawing machine 20 is substantially closed by means of the generally U-shaped catch pans 30, which are formed as coolers and are positioned so as to catch broken glass which may drop in the machine and thus prevent entry of fragments into the bath 12. These catch pans 30 also extend substantially to the end walls 28 of the kiln 13 and are constructed for the passage of cooling fluid, such as water; One leg of each catch pan 30 is disposed substantially parallel toand spaced from the sheet 10. Conventional water coolers 32 are provided for cooling sheet 10 by absorbing radiation from the sheet 10. The coolers 32 are spaced above the surface of the bath 12 and are positioned on opposite sides of the sheet 10 to extend substantially the width of the sheet.

So much of the apparatus as has been just described in common to the prior art and the instant invention and constitutes a normal -or usual sheet glass drawing apparatus setup.

Reference is now made to FIG. 2 illustrating a basic embodiment of this invention wherein, in addition to the conventional apparatus elements in their usual structural arrangement, there are gas current injecting means, such as burners 40, extending substantially the width of the plane of draw of the glass sheet and positioned on the upper surface 44 of a foot portion 43 of each L-block. There is also a backing, such as sheet material 36, fastened to the back surface of each cooling member 32, which will be described more fully in connection with FIGS. 6 and 7.

The burners are pipes, each having closely spaced holes through which gas under pressure, such as combustible fluid, can escape, preferably normal to the longitudinal axis of the pipes. Upon combustion, the gaseous products form a substantially continuous sheet of heated gases extending across the chamber 22. The burners 40 4- are illustrated as having their flames directed upwardly at an inclined angle toward sheet 10, but the burners are so constructed as to be rotatable about their major axes to vary the inclined angle of the flames.

FIG. 3 illustrates a second embodiment of the invention wherein the burners 40 have been positioned within a recess 42 extending the length of the foot portion 43 of each L-block 24. The recesses 42 are preferably of sufficient depth so that the burners 40 do not extend above the upper surface 44 of the foot of each L-block. Structural details of the recessed L-block are illustrated in FIG. 5 and will be later discussed. In this embodiment there is no backing on the coolers 32.

FIG. 4 illustrates a third embodiment of the invention wherein the desirable features of the first two embodiments have been combined. Thus, the conventional coolers 32 are provided with a sheet material backing 36, and the burners 40 are positioned within the recesses 42 of L'blocks 24.

FIG. 5 illustrates constructional details of the L-block 24and the recess 42. Details of the drawing apparatus, such as the drawing chamber, are omitted for the sake of clarity.

FIG. 6 illustrates constructional details of one form of cooling member, including the mounting means for attaching a backing. The illustrated backing, in the form of a flat, pressed sheet of asbestos-type material 36, rests on a rearwardly extending foot portion 33 of each cooler 32, and is preferably fastened at the top of each cooler by angle backets 38. These brackets are suitably fastened, as by welding, to the top of each cooler 32 to provide a channel which allows the backing material to be slid into place from either end of the cooler. The pipes 34 provide for continuous circulation of water through the cooling member, in a manner well known in the art.

In FIGS. 1 to 4, inclusive, of the drawings, the directions of the principal air currents within the drawing chamber 22 are shown by arrows for the right-hand portion of chamber 22. It is not necessary to show the principal air currents to the left of sheet 10 because they are mirror images of those shown. Relatively high, intermediate, and relatively low velocity air currents are shown in heavy solid, light solid, and broken lines, respectively.

In FIG. 1 the principal air currents for the normal drawing kiln arrangement are illustrated. The temperature of glass sheet 10 in its travel through chamber 22 is substantially above the general air temperature within chamber '22, so that sheet 1% induces air to flow in the direction of its draw and along its faces. This air flow creates low pressure zones in the vicinity of each side of the base 16 of sheet 10. The current of air along the faces of the sheet are those which form the natural stack effect. This layer of air along the sheet moves at a substantially greater velocity than the sheet. To supply this stack flow of air there must be a supply of air flowing to the low pressure Zones. A primary source of this air is the drawing machine. That air enters chamber 22 between sheet 10 and catch pans 30 at a temperature below that of sheet 10 and flows past the catch pans 30, which are constructed as coolers, the ventilator coolers 26 and the L-blocks 24 between the end walls 28, all at a relatively low temperature, so that a zone on each side of sheet 10 and generally bounded by catch pan cooler 30, ventilator cooler 26, L-block 24 and walls 28 becomes a secondary source of colder air. The temperature in this secondary zone will vary transversely thereof, being lower adjacent the end walls 28, so that air in different portions in this zone will also vary in temperature. Air from this zone flows to the low pressure zone at the base 16 on each side of sheet 10. The colder air from the secondary source flows downwardly and across both faces of coolers 32, being further chilled, and into the low pressure zone at the base of sheet 10, thereby providing a relatively large quantity of colder air and, more importantly, moving at relatively high velocities of dilferent magnitudes to the low pressure zone. This colder air of different temperatures and velocities transversely of chamber 22 disturbs non-uniformly the air traveling with the sheet, resulting in the formation of the usual characteristic longitudinal wave pattern extending in the direction of the draw. Endaround currents of colder air also flow to the low pressure zones at the base 16 of sheet and disturb the air flowing with the sheet in the direction of-the draw, thus re sulting in the diagonal wave pattern.

In accordance with the present invention (referring to FIG. 2 which shows the arrangement utilizing burners and backed coolers) a backing, such as a sheet of insulating material, is secured to the back surface (facing away from the plane of draw) of each cooler in a suitable manner previously explained in conjunction with FIG. 6. This backing not only prevents the air behind the coolers from contacting the surface thereof and being cooled by conduction, but it also, and more importantly, absorbs heat emanating from the molten bath and from the front face of the foot of each L-block (which, by virtue of its proximity to the molten bath, has attained an elevated temperature) and transfers this heat by conduction to the surrounding air thus forming, in effect, a localized source of heat. Due to the location and the vertically extending planar configuration of the backing, it is ideally suited to create a strong upwardly directed stack of hot air behind the entire area of each cooler. It can be seen that this second stack flows in the same direction as the normal stack adjacent the glass sheet being drawn, but is displaced therefrom so as to counteract the cyclical movement of air from the secondary source of cold air which normally moves toward the base 16.

In addition to the backing on each cooler, burners 40, shown as having their flames angularly directed away from the L-blocks 24, have been placed on the top surface of the foot of each L-bl'ock to further alter or divert the path of movement of air in the zone of the secondary source of air, giving a cyclical path to this air. The burners 40 create zones of low pressure adjacent their locations so that air from the vicinity of the coolers 32, including that which may cascade downwardly across the front surface (facing the plane of draw) and would then normally flow to the base 16, will be drawn underneath and behind the coolers away from the base and into the second stack created by the backing on the coolers. In addition, the air flowing down the cooler upright portions of the L-blocks and along the foot portions thereof toward the base of the glass sheet will also be directed upwardly behind the coolers and into the second stack. Since the air flowing toward base 16 of sheet 10 is materially reduced, the effects of its non-uniformity in velocities and temperature does not disturb the relatively thin surface adhering film of air adjacent the sheet. Because this fiow of air to the base 16 of the sheet 10 is not entirely eliminated, air still flows in the direction of the draw as the protective envelope. However, some of this air has been diverted into the cyclic path of movement of the air in the zone of the secondary source and is rendered ineffective to disturb the film of air adjacent the sheet 10.

As far as the end-around currents are concerned, these are drawn into the cyclic path of movement of the air in the zone of the secondary source and are rendered substantially ineffective to disturb the relatively thin surface adhering film of air adjacent the sheet. The overall effect is the material reduction or elimination in intensity .of the usual wave patterns.

FIG. 3 shows the arrangement with the conventional coolers, but with the burners 40 positioned in recesses 42 in the foot portion 43 of each L-block. The effect of these burners upon the air currents within the drawing chamber is shown by the arrows in FIG. 3. The burners 40 create zones of low pressure adjacent their locations so that air flowing down the front surface of each cooler will be drawn under and behind the cooler, while that air flowing down the back surface will be diverted by the rising column of warmer air from the burner into the cyclic path of movement of the air within the zone of the secondary source. While such an arrangement does not control air currents to the extent-obtained with a combination of a gas injecting means and a backing on the coolers, there is a material improvement over the currents in a conventional drawing chamber arrangement as illustrated in FIG. 1. The arrangement shown in FIG. 3 is useful in producing a high quality, medium grade glass at a substantially higher production rate and thus at a lower cost than glass drawn using the arrangement of FIG. 2. This is because -a backing on the coolers, as in the embodiment of FIG. 2, absorbs and transfers to the surrounding air heat radiated from the molten bath and from the front face of the foot of each L-block, which heat would normally be absorbed by the back surface of the cooler. As a result, the temperature within such a drawing chamber is increased to a significant extent over a drawing chamber in which the coolers have no backing, as in the instant embodiment. Since an increase in the temperature within the drawing chamber lowers the rate at which the glass sheet solidifies, the drawing speed, and hence the quantity of glass produced, must be accordingly diminished to assure sufiicient solidification of the sheet prior to its exit from the drawing chamber.

The substantial improvement in the results achieved by the use of the embodiment of FIG. 3, as compared with the conventional drawing chamber as illustrated in FIG. 1, may be attributed to a significant extent to the recessed portion in the top surface of the foot of each L-block in which the gas current injecting means are located. As may be seen from FIG. 3, the recess lowers the position of each burner, permitting the low pressure areas produced by the burners to influence the air currents flowing down the front surface and underneath each cooler at an earlier point in their cycle of flow. Thus, these air currents are not only drawn underneath the coolers, but they are also caused to flow in a horizontal direction along the surface of the bath toward the front face of the foot of each L-block before they begin to rise under the influence of the burners. Because the path of the air has been diverted closer to the burners than in the embodiment where the burners are positioned above the top surface of the foot of each L-block, the burners may exert a maximum effect upon the air and therefore create a stronger stack than if the burners were located in a higher position. In addition, burners 40, by virtue of their position below the top surface of the foot of the L-block, are substantially protected from the flow of cyclic air currents in the secondary source of air. Therefore, as these currents descend along the surface of the L-block toward the low pressure area formed by the burners 40, as shown by the arrows in FIG. 3, they will pass above the burners and be directed upwardly by the rising warmer gases from the burner rather than be allowed to descend into and pass through the burner area, disturbing the even flame pattern and uniform stack effect necessary for proper control. Furthermore, the recess serves to locate the burner at the optimum position, properly aligned for controlling the air currents within the drawing chamber. Heretofore, consistent results have been difficult to obtain from different drawing kilns, even though located on the same melting tank. Although the geometry of the drawing chamber is similar in each kiln, the variations in operating procedures by the different operators in charge of each kiln, the different location of each drawing chamber relative to the melting tank, the different location of each tank relative to the building in which it is housed, and the existence of small air leaks in the walls of the drawing chambers are believed to be the major factors contributing to the inconsistent results produced in different drawing chambers. These factors necessitate a slightly different setting of each burner if the burners are merely placed on the surface of the foot of each L-block, as would be required with conventional L- blocks. In the instant embodiment, substantially uniform results have been achieved in various drawing chambers in spite of the differences enumerated above and without critical, individual adjustments being made within each chamber, by placing the gas current injecting means, such as burners 40, in a recessed portion of the foot of each L-block. The gas current injecting means is in this way properly located and substantially shielded from the high velocity currents of the secondary source of cold air within the drawing chamber (which currents vary in different drawing chambers under the influence of some of the above-mentioned factors) and may therefore supply a more uniformly directional stack effect at a more constant temperature than if located above the surface of the foot of the L-block. This improved result may be observed, in the case of burners recessed in the foot of each L-block, by noting the constant angle of the flame across the entire width of the drawing chamber. On the other hand, the flame of a burner placed above the surf-ace of an L-block may be observed to vary its angle under the influence of the non-uniform air currents within the drawing chamber, and to different extents in different chambers.

In FIG. 4, there is shown an arrangement similar to FIG. 3, with the addition of a sheet material backing 36 on the cooling members 32 in a similar manner to that shown in FIG. 2. This arrangement has been found to be most effective in eliminating the formation of an objectionable wave pattern, since it combines the desirable pattern controlling features of the two previous embodiments. A sheet material backing has been applied to the coolers to create a stack of rising warmer air behind each cooler in the same manner as in the embodiment of FIG. 2. In addition, the gas injecting means, such as burners 40, have been recessed in the foot portion .of each L-block, to provide a properly located and relatively undisturbed flame pattern. The cumulative effect of these two features is to effectively divert and control the cooler air currents within the drawing chamber so as to allow an even rate of cooling of the sheet of glass substantially entirely by radiation, thereby virtually eliminating the undesirable wave pattern customarily found in drawn glass.

Generally speaking, for optimum results, the burners should have their flames directed from the vertical at an angle of approximately 45 degrees toward sheet 10; and when the L-block is not recessed, as in conventional L- blocks, the burners are preferably placed on the outermost edge or lip of the foot portion 43 of the L-blocks.

FIG. 5 shows in detail an L-block 24 for accommodating a burner or other gas injecting means within the drawing chamber. The L-block is comprised of a suitable refractory material formed with two mutually perpendicular members 41 and 43 which are substantially coextensive in width. One member or horizontal foot portion 43, adapted to be positioned horizontally above the molten bath of glass, is substantially shorter than the other member or upright portion 41 which is adapted to form vertical walls along the width of the drawing chamber. The longer, normally vertical, member 41 includes a conventional cut-out portion 45 along thewidth of the upper, inner corner thereof to receive the ventilator coolers 26, as shown in FIG. 2. The shorter foot portion 43, in accordance with this invention, has been provided with a recess 42 in the top surface 44 thereof and extending the entire width of, but of less depth than, the foot portion.

Except for a small section 46 at each side of the foot por-' tion, the recess preferably extends to the front surface of the foot (see FIG. 5) so as to provide an unobstructed path for the injected gas. Alternatively, the recess may be located a short distance from the front lip of the foot of the L-block, so as to form a recess bounded by the refractory on three sides instead of on only two. Where the notch extends to the front surface of the foot, as illustrated, side portions 46 adequately restrain the gas injecting means within the notch 42 and yet facilitate ready adjustment and replacement thereof.

It should be understood, of course, that the foregoing disclosure relates to only preferred embodiments of the invention and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention.

I claim:

A refractory L-block member, for use as a defining wall of a glass drawing kiln and entirely above a pool of molten glass, having two mutually perpendicular portions, the length of one normally extending in a vertical direction, the length of the other normally extending in a horizontal direction, both of said portions being substantially coextensive in width, the vertical length of said member being greater than the horizontal length thereof to provide said defining wall, the width being of greater magnitude than the thickness .of either of said portion-s, and a recess contained in the upper surface of the normally horizontally extending portion of the refractory member at the outermost edge thereof, said recess being of lesser dimension than the length or thickness of the containing portion but extending substantially the Width thereof and substantially parallel to the otherv of said portions.

References Cited by the Examiner UNITED STATES PATENTS 1,538,169 5/1925 Conklin 65-343 FOREIGN PATENTS 671,070 1/1939 Germany. 245,449 8/ 1926 Great Britain. 525,898 9/1940 Great Britain. 768,741 2/1957 Great Britain.

DONALL H. SYLVESTER, Primary Examiner.

S. LEON BASHORE, D. CRUPAIN,

Assistant Examiners. 

